Beepre voltage question

[Paul Birkeland]

As long as you have 0V on pin 3 of the 4 pin sockets, then there isn't any concern for unusual operation conditions due to grid voltage variations.

It might also be good to ensure that the tubes are making good contact with the socket pins.

-PB

[Jamus]

Tubes do seem to be making good contact but I'm not really sure how to confirm it.

I noticed a new problem that wasn't there yesterday. The two LEDs on the C4S board, B side, near the front of the chassis light up on start up but then quickly go out. (Edit: perhaps not completely out but very faint)

[Paul Birkeland]

You might try reheating the center legs of all the MJE5731A's.  These can be tough to get a good solder joint on, and you practically cannot overheat these transistors when soldering them, especially on the center legs.

[Jamus]

Now that you mention it a few of those did look a little suspect. I reflowed them all but no change in the voltages or the LEDs dimming on the B side.

[Paul Birkeland]

You can also try poking around with a wooden chopstick to see if you can find the suspect connection that is causing this problem.

-PB

[Jamus]

Just another observation in case it helps in diagnosing this problem. The voltage at these four terminals in question spikes to 215v when the unit is powered on, then they all settle at 142v within a few seconds.

Also, the issue with the B channel LEDs dimming once the tubes heat up moved to the A channel when I switched tubes. This is still on the "B side" of the C4S board and they are still lit, just faintly.

[Paul Birkeland]

Just another observation in case it helps in diagnosing this problem. The voltage at these four terminals in question spikes to 215v when the unit is powered on, then they all settle at 142v within a few seconds.

This is the EL84/TL31 regulator powering on and doing its job.

Just out of curiosity, did this BeePre ever work properly?  (I had assumed it did, but I'm realizing that this might be an error)

[Jamus]

I got replacement tubes today and rechecked voltages. Now all 4 relevant terminals (2, A2, 17, B2) all measure 121v. This is only 10% over spec (90-110v) so I assume this is okay (?). All other voltages were within spec.

Next I hooked up CD player and BH crack to listen. All sounded great at first, listened for about 5 minutes. I left it playing for about 30 minutes to continue warming up. When I came back to listen there was almost no volume.

I took the BeePre out of the chain and the Crack works fine. I let everything cool down for a few minutes (top plate on BeePre was very hot). When I fired everything back up it sounded normal for about 5 seconds, then volume dropped down again.

Any suggestions on where to start with troubleshooting?

Only for less than 30 minutes 

[Jamus]

Just going back over the manual step by step looking for any possible errors on my part. On the C4S boards does it matter which 2 out of 3 bB terminal holes are used for black wires?

[Paul Birkeland]

Ah, OK, I should've picked up on that before I had you send off the tubes.  This is almost certainly flaky solder joints in the build, I would just reheat absolutely all of them.  Also be sure that all the heasink hardware is on tightly.

-PB

[Jamus]

Welp, I just finished reflowing every joint in the entire kit and I still get the same 142v at those 4 terminals. I also went step by step through the manual to be sure I didn't miswire anything. Any other ideas?

[Jamus]

Just going back over the manual step by step looking for any possible errors on my part. On the C4S boards does it matter which 2 out of 3 bB terminal holes are used for black wires?

Just want to rule this out as a possible source of the problem. Are there 3 bB terminal holes on the C4S boards and we are using 2 of them or am I misunderstanding the manual on that? If so, does it matter which 2 we use (adjacent holes) or are they all connected anyways?

[Chris65]

The three bB pads are connected.
Some photos of your build may help, another pair of eyes can often spot a mistake that you missed.

[Jamus]

Thanks Chris!
My next plan of attack was to poke around with a wood chopstick while measuring DC volts at the offending terminals. I figure if I see any improvement in the conduction I'll know where to concentrate my efforts.

It was such a downer after reflowing and rechecking every single terminal to see no improvement whatsoever but it helps to know there is such a supportive community on here ready to help.

Thanks,
Jamus

[Jamus]

I tried probing most terminals while measuring volts at both terminal 2 and 17. Neither budged from 142v while I probed away. I don't think that rules out a flakey connection but after reflowing all terminals I'm starting to lean away from that as the cause (I could be wrong of course!).

I did notice that on the C4S boards, both inboard heatsinks were very hot to the touch while both outboard heatsinks were room temp. Is that normal or could that be a clue to the source of the problem?

Since both sides of the unit are affected I'm wondering if there are any fragile transistors or resistors on either PC boards I could have fried during the build which I could imagine doing twice if I'm using the same bad technique.

Any ideas for next steps? I'll upload some photos if that would help, any particular areas to focus on?